Safety Margins for Geometrical Uncertainties in Radiotherapy

Cancer is the unrestricted growth of cells in an organism, which can eventually destroy organs that are needed for survival of the organism. Throughout human history, cancer has been one of the major medical causes of death. At the moment, there are about 840.000 cancer fatalities in Europe per year. It is estimated that in the westem world approximately 1 in 3 people will develop some kind of tumor during their lifetime, and more than 1 in 5 will die of it. Although significant progress has been achieved in the fight against cancer in the last decades, still about half of the cancers cannot be cured. Currently, the three main therapies for cancer are surgery (removing the tumor), radiotherapy (killing the tumor cells with radiation), and chemotherapy (the use of anti-cancer mugs). The first two are especially used for tumors that are well localized. Surgety is straightforward but catmot always be applied, for instance when the tumor is localized in or close to a vital organ. Futthermore, invisible, microscopic extensions of the tumor might be trtissed. In radiotherapy, those tumor extensions can be treated more easily. Moreover, this therapy may be less demanding on the patient and hospitalization is usually not necessaty. When microscopic tumor cells have spread from the primary tumor site to different parts of the body, chemotherapy can be applied. The blood circulation is used to transpoti the drugs are transported through the body. In many cases, the difterent therapies are combined to improve the treatment outcome. Radiotherapy is used for about half of all cancer patients. With radiotherapy, ionizing radiation in the fotm of high energy photons, electrons or protons is aimed at the tumor. These particles deposit some of their energy in the tumor cells, which can cause ionization of DNA or surrounding molecules. This can induce irreparable genetic damages in the tumor cells that either kill the cell directly or result in the socalled apoptosis, i.e. cellular suicide. However, since radiation may kill healthy cells as well, one has to be careful to deliver the radiation dose in the right place. Basically, there are two ways the radiation can be delivered: by brachytherapy or by external beam radiotherapy

MR-ONLY as a reference image in verifying positioning in radiotherapy

Introdução: Os sistemas de planeamento utilizam a informação das densidades eletrónicas, necessárias para o cálculo de dose provenientes da TC. Uma tendência recente é o uso da RM como única modalidade, usando as imagens de RM para criar uma TC sintética. Um fluxo de trabalho no qual todas as etapas pré-tratamento são realizadas na RM é favorável. O objetivo do estudo é validar a técnica MR-Only como imagem de referência na verificação do posicionamento em Radioterapia. Metodologia: Foram incluídos 13 doentes com tumor cerebral e 15 doentes com tumor retal, seguidos no Serviço de Radioterapia do Centro Clínico Champalimaud, de outubro de 2019 a junho de 2020. Com base no registo automático de 80 CBCT comparou-se os desvios entre as imagens da TC de planeamento e da TC sintética (MR-Only). Resultados: No registo das imagens do reto, a variação que se obteve foi inferior a 1,4mm longitudinal, 1mm lateral e vertical. A variação nas translações foi de -0,2±0,3mm lateral, -0,3±0,4mm vertical e de -0,4±0,7mm longitudinal. As rotações foram inferiores a 0,4º, sendo a variação verificada 0,0±0,2º pitch, 0,0±0,1º yaw e de 0,0±0,1º roll. No cérebro foi inferior a 1,3mm longitudinal, a 0,6mm vertical e a 0,4mm lateral. A variação verificada foi de -0,2±0,2mm lateral, -0,3±0,2mm vertical e de -0,4±0,5mm longitudinal. Nas rotações, obteve-se uma rotação máxima de 0,3º, sendo a variação verificada -0,2±0,1º pitch, 0,1±0,1º yaw e de 0,0±0,1º roll. Conclusão: Foi validado o registo da imagem da TC sintética com a imagem de verificação CBCT. Os desvios encontrados nos registos entre a TC de planeamento e a TC sintética da RM sugerem que é justificado o uso da técnica MR-Only como imagem de referência.ABSTRACT - Introduction: The planning systems use the information of the electronic densities, needed for the calculation of the dose from the CT. A recent trend is the use of MR as the only modality, using the MR image to create a synthetic CT. A workflow in which all pre-treatment steps are performed at the MR is favorable. The objective of this study is to validate the MR-Only technique as the reference image in the verification of positioning in Radiotherapy. Materials and Methods: 13 patients with a brain tumor and 15 patients with a rectal tumor followed at the Radiotherapy Unit of the Champalimaud Clinical Center, from October 2019 to June 2020, were included. Based on the automatic registration of 80 CBCT, the deviations between images of planning CT and synthetic CT (MR-Only) were compared. Results: In the registration of the images in the rectum, the variation that was obtained was less than 1,4mm longitudinal, 1mm laterally, and vertically. The variation verified in the translations was - 0,2±0,3mm lateral, -0,3±0,4mm vertical, and - 0,4±0,7mm longitudinal. Regarding rotations were lower than 0,4º, with the variation verified 0,0±0,2º pitch, 0,0±0,1º yaw, and 0,0±0,1º roll. In the brain it was less than 1,3mm longitudinally, 0,6mm vertically and 0,4mm laterally. The variation found was -0,2±0,2mm lateral, -0,3±0,2mm vertical, and -0,4±0,5mm longitudinal. In the rotations, a maximum rotation of 0,3º was obtained, being the variation verified -0,2±0,1º pitch, 0,1±0,1º yaw, and of 0,0±0,1º roll. Conclusion: The registration of the synthetic CT image with the CBCT verification image was validated. The minimum deviations found in the results between the planning CT and the synthetic CT of the MRI suggest that the use of the MR-Only technique as a reference image is justified.info:eu-repo/semantics/publishedVersio

High-precision prostate cancer irradiation by clinical application of an offline patient setup verification procedure, using portal imaging

Purpose: To investigate in three institutions, The Netherlands Cancer Institute (Antoni van Leeuwenhoek Huis [AvL]), Dr. Daniel den Hoed Cancer Center (DDHC), and Dr. Bernard Verbeeten Institute (BVI), how much the patient setup accuracy for irradiation of prostate cancer can be improved by an offline setup verification and correction procedure, using portal imaging. Methods and Materials: The verification procedure consisted of two stages. During the first stage, setup deviations were measured during a number (N(max)) of consecutive initial treatment sessions. The length of the average three dimensional (3D) setup deviation vector was compared with an action level for corrections, which shrunk with the number of setup measurements. After a correction was applied, N(max) measurements had to be performed again. Each institution chose different values for the initial action level (6, 9, and 10 mm) and N(max) (2 and 4). The choice of these parameters was based on a simulation of the procedure, using as input preestimated values of random and systematic deviations in each institution. During the second stage of the procedure, with weekly setup measurements, the AvL used a different criterion ('outlier detection') for corrective actions than the DDHC and the BVI ('sliding average'). After each correction the first stage of the procedure was restarted. The procedure was tested for 151 patients (62 in AvL, 47 in DDHC, and 42 in BVI) treated for prostate carcinoma. Treatment techniques and portal image acquisition and analysis were different in each institution. Results: The actual distributions of random and systematic deviations without corrections were estimated by eliminating the effect of the corrections. The percentage of mean (systematic) 3D deviations larger than 5 mm was 26% for the AvL and the DDHC, and 36% for the BVI. The setup accuracy after application of the procedure was considerably improved (percentage of mean 3D deviations larger than 5 mm was 1.6% in the AvL and 0% in the DDHC and BVI), in agreement with the results of the simulation. The number of corrections (about 0.7 on the average per patient) was not larger than predicted. Conclusion: The verification procedure appeared to be feasible in the three institutions and enabled a significant reduction of mean 3D setup deviations. The computer simulation of the procedure proved to be a useful tool, because it enabled an accurate prediction of the setup accuracy and the required number of corrections

Using histopathology breast cancer data to reduce clinical target volume margins at radiotherapy

This study aimed to quantify the incidence and extension of microscopic disease around primary breast tumors in patients undergoing breast-conserving therapy (BCT), focusing on a potential application to reduce radiotherapy boost volumes. An extensive pathology tumor-distribution study was performed using 38 wide local excision specimens of BCT patients. Specimen orientation was recorded and microscopic findings reconstructed to assess the incidence of microscopic disease around the macroscopic tumor. A model of disease spread was built, showing probability of disease extension outside a treated volume (P(out,vol)). The model was applied in 10 new BCT patients. Taking asymmetry of tumor excision into account, new asymmetric margins for the clinical target volume of the boost (CTV(boost)) were evaluated that minimize the volume without increasing P(out,TTV) (TTV being total treated volume: V(surgery) + CTV(boost)). Potential reductions in CTV(boost) and TTV were evaluated. Microscopic disease beyond the tumor boundary occurred isotropically at distances > 1 cm (intended surgical margin) and > 1.5 cm (intended TTV margin) in 53% and 36% of the excision specimens, respectively. In the 10 prospective patients, the average P(out,TTV) was, however, only 16% due to larger surgical margins than intended in some directions. Asymmetric CTV(boost) margins reduced the CTV(boost) and TTV by 27% (20 cc) and 12% (21 cc) on average, without compromising tumor coverage. Microscopic disease extension may occur beyond the current CTV(boost) in approximately one sixth of patients. An asymmetric CTV(boost) that corrects for asymmetry of the surgical excision has the potential to reduce boost volumes while maintaining tumor coverag

The effect of age in breast conserving therapy : A retrospective analysis on pathology and clinical outcome data

Background and propose: Age is an important prognostic marker of patient outcome after breast conserving therapy; however, it is not clear how age affects the outcome. This study aimed to explore the relationship between age with the cell quantity and the radiosensitivity of microscopic disease (MSD) in relation to treatment outcome. Materials and methods: We employed a treatment simulation framework which contains mathematic models for describing the load and spread of MSD based on a retrospective cohort of breast pathology specimens, a surgery simulation model for estimating the remaining MSD quantity and a tumor control probability model for predicting the risk of local recurrence following radiotherapy. Results: The average MSD cell quantities around the primary tumor in younger (age Conclusion: The higher local recurrence rate in younger patients could be explained by larger clonogenic microscopic disease cell quantity, even though the microscopic disease cells were found to be more radiosensitive. (c) 2015 Elsevier Ireland Ltd. All rights reserved